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What is melanoma skin cancer?

Melanoma is a cancer that starts in a certain type of skin cell. To understand melanoma, it helps to know a little about the skin.

Normal skin

The skin is the largest organ in the body. It does many different things, such as:

Covering and protecting the organs inside the body

Helping to keep out germs

Helping keep in water and other fluids

Helping control body temperature

Protecting the rest of the body from ultraviolet (UV) rays

Helping the body make vitamin D

The skin has 3 layers. From the outside in, they are:

Epidermis: This top layer of the skin is very thin. The flat cells at the top of this layer are called squamous cells. Below this are cells called basal cells. Cells called melanocytes are also in the epidermis. These cells make the brown pigment melanin, which gives the skin its tan or brown color. Melanocytes are the cells that can become melanoma.

Dermis: This middle layer of the skin is much thicker than the epidermis. It contains hair shafts, sweat glands, blood vessels, and nerves.

Subcutis: This deepest layer of the skin contains proteins and fat, which help keep in body heat and act as a shock absorber to help protect the body’s organs from injury.

Skin tumors that are not cancer

Most skin tumors are not cancer (they are benign). These rarely, if ever, turn into cancer. Some of them include:

Mole (also called a nevus) – a benign skin tumor that starts from melanocytes. Almost everyone has some moles. Nearly all of them are harmless, but some types can raise your risk of melanoma.

Hemangioma – a benign blood vessel growth often called a strawberry spot or port wine stain

Lipoma – a soft growth made up of fat cells

Wart – a rough-surfaced growth caused by a virus

Melanoma skin cancers

Melanoma is a cancer that begins in the melanocytes. Because most of these cells still make melanin, melanoma tumors are often brown or black. But this is not always the case, and melanomas can also appear pink, tan, or even white.

Melanoma most often starts on the trunk (chest or back) in men and on the legs of women, but it can start in other places, too. Having dark skin lowers the risk of melanoma, but a person with dark skin can still get melanoma.

Melanoma is much less common than basal cell and squamous cell skin cancers (described below), but it is far more dangerous. It can almost always be cured in its early stages. But it is likely to spread to other parts of the body if it is not caught early.

Other skin cancers

Skin cancers that are not melanoma are sometimes grouped together as non-melanoma skin cancers because they start in skin cells other than melanocytes.

Basal cell and squamous cell cancers are much more common than melanoma. Because they rarely spread to other parts of the body, these cancers are often less worrisome and are treated differently than melanoma. They are discussed in our document Skin Cancer: Basal and Squamous Cell.